This invention relates to RFID reader systems. More particularly, the invention relates to RFID reader systems in which the reader's antenna system may be in an unknown orientation, may be moving, or may be pointing in an unknown direction. For example, in many fixed-reader installations, a reader's antenna can be installed “right side up”, “upside down”, or “sideways” either at the discretion of the installer because of physical constraints such as insufficient space for mounting in a preferred orientation, or because the reader's antenna must be mounted on a moving element, such as a mechanical arm or rotating joint. In these cases, the polarization or radiation pattern of the reader's antenna may not be optimal given the polarization or spatial distribution of the tags to be read by the reader system. In situations in which it is not practical to use manual intervention to physically move the reader's antenna to a new orientation or location, it is therefore desirable for the reader's antenna system to be dynamically and automatically reconfigured.
In another aspect, this invention is particularly applicable to handheld or mobile RFID reader installations in which an RFID reader is either carried by a human, or carried by a vehicle in motion. In these cases, the physical motion of the reader's antenna system may not result in optimal reading of a particular group of tags. For example, if a handheld reader system has a linearly polarized antenna and is being used to read linearly polarized tags, the orientation of the handheld reader must be maintained in a preferred orientation (reader antenna polarization axis parallel to tag antenna polarization axis) to ensure best tag reading performance. Holding a reader in such a position may lead to repetitive stress injuries, or simply to operator fatigue over time. Alternatively, if an operator has a preferred handedness different from the one for which the handheld reader was designed, or if the operator has a disability preventing careful control over the motion of the handheld reader, the operator may have difficulty continuously pointing the reader's antenna in the proper direction for optimal tag reading. In this case too, it is desirable for the reader's antenna system to be dynamically reconfigured by an automated system.
According to presently preferred embodiments of the invention, the RFID reader system takes as input an external sensor reference for physical orientation and/or pointing direction and/or motion, and dynamically adjusts the reader's antenna system in response thereto. This dynamic adjustment may be made by means of switching antenna polarization, switching between antenna elements having different radiation patterns, or electrically steering a steered-beam antenna to a preferred direction to maintain optimal RFID reading performance.
Currently, in the case of fixed RFID readers, the reader's antenna is mounted at the time of installation in a fixed manner to a particular surface, which may be either static or moving. This antenna mounting is then not changed unless a problem with the reader system's performance is noted, and then a maintenance worker must be dispatched to readjust the antenna's mounting and once again affix it in the predetermined proper position. In the case of an RFID reader antenna mounted to a moving arm or piece of machinery, a non-optimal antenna polarization or pointing angle may well be accepted even though it results in suboptimal RFID system performance.
For handheld RFID-enabled computers, the reader's antenna is affixed in a particular orientation to the body of the handheld device, and the user is expected to move his or her hands, arms, or body appropriately to maintain a fixed orientation of the antenna with respect to a population of RFID tags being read. This often results in poor ergonomics and an awkward motion for the operator.
RFID reader systems according to embodiments of the present invention automatically compensate for the motion of the operator to allow for use of comfortable movements that do not cause repetitive strain injuries or other difficulties.
For vehicle mounted RFID readers, the motion of the vehicle is dynamically cancelled out by electrically steering either the beam polarization or radiation pattern in order to maintain optimal RFID performance.